'\" te
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.TH UMEM_DEBUG 3MALLOC "Dec 9, 2017"
.SH NAME
umem_debug \- debugging features of the umem library
.SH SYNOPSIS
.nf
\fBcc\fR [ \fIflag\fR\&.\|.\|. ] \fIfile\fR\&.\|.\|. \fB-lumem\fR [ \fIlibrary\fR\&.\|.\|. ]
#include <\fBumem.h\fR>
.fi

.SH DESCRIPTION
The \fBlibumem\fR library provides debugging features that detect memory leaks,
buffer overruns, multiple frees, use of uninitialized data, use of freed data,
and many other common programming errors. The activation of the run-time
debugging features is controlled by environment variables.
.sp
.LP
When the library detects an error, it writes a description of the error to an
internal buffer that is readable with the \fB::umem_status\fR \fBmdb\fR(1)
\fIdcmd\fR and then calls \fBabort\fR(3C).
.sp
.LP
When using the debugging features of the library, a program may opt into
changing the failure rate of memory allocation. This is often useful for
test code that would like to force memory allocation failures in a
controlled fashion. See the \fBumem_setmtbf\fR(3MALLOC) function for
more information.
.SH ENVIRONMENT VARIABLES
.ne 2
.na
\fB\fBUMEM_DEBUG\fR\fR
.ad
.RS 16n
This variable contains a list of comma-separated options.  Unrecognized options
are ignored. Possible options include:
.sp
.ne 2
.na
\fB\fBaudit\fR[=\fIframes\fR]\fR
.ad
.RS 20n
This option enables the recording of auditing information, including thread ID,
high-resolution time stamp, and stack trace for the last action (allocation or
free) on every allocation.  If transaction logging (see \fBUMEM_LOGGING\fR) is
enabled, this auditing information is also logged.
.sp
The \fIframes\fR parameter sets the number of stack frames recorded in the
auditing structure. The upper bound for frames is implementation-defined. If a
larger value is requested, the upper bound is used instead.
.sp
If \fIframes\fR is not specified or is not an integer, the default value of 15
is used.
.sp
This option also enables the \fBguards\fR option.
.RE

.sp
.ne 2
.na
\fB\fBcontents\fR[=\fIcount\fR]\fR
.ad
.RS 20n
If auditing and contents logging (see \fBUMEM_LOGGING\fR) are enabled, the
first \fIcount\fR bytes of each buffer are logged when they are freed.  If a
buffer is shorter than \fIcount\fR bytes, it is logged in its entirety.
.sp
If \fIcount\fR is not specified or is not an integer, the default value of 256
is used.
.RE

.sp
.ne 2
.na
\fB\fBdefault\fR\fR
.ad
.RS 20n
This option is equivalent to \fBaudit\fR,\fBcontents\fR,\fBguards\fR.
.RE

.sp
.ne 2
.na
\fB\fBguards\fR\fR
.ad
.RS 20n
This option enables filling allocated and freed buffers with special patterns
to help detect the use of uninitialized data and previously freed buffers. It
also enables an 8-byte redzone after each buffer that contains
\fB0xfeedfacefeedfaceULL\fR.
.sp
When an object is freed, it is filled with \fB0xdeadbeef\fR.  When an object is
allocated, the \fB0xdeadbeef\fR pattern is verified and replaced with
\fB0xbaddcafe\fR.  The redzone is checked every time a buffer is allocated or
freed.
.sp
For caches with either constructors or destructors, or both,
\fBumem_cache_alloc\fR(3MALLOC) and \fBumem_cache_free\fR(3MALLOC) apply the
cache's constructor and destructor, respectively, instead of caching
constructed objects. The presence of \fBassert\fR(3C)s in the destructor
verifying that the buffer is in the constructed state can be used to detect any
objects returned in an improper state.  See \fBumem_cache_create\fR(3MALLOC)
for details.
.RE

.sp
.ne 2
.na
\fB\fBverbose\fR\fR
.ad
.RS 20n
The library writes error descriptions to standard error before aborting. These
messages are not localized.
.RE

.RE

.sp
.ne 2
.na
\fB\fBUMEM_LOGGING\fR\fR
.ad
.RS 16n
To be enabled, this variable should be set to a comma-separated list of
in-memory logs. The logs available are:
.sp
.ne 2
.na
\fB\fBtransaction\fR[=\fIsize\fR]\fR
.ad
.RS 22n
If the \fBaudit\fR debugging option is set (see \fBUMEM_DEBUG\fR), the audit
structures from previous transactions are entered into this log.
.RE

.sp
.ne 2
.na
\fB\fBcontents\fR[=\fIsize\fR]\fR
.ad
.RS 22n
If the \fBaudit\fR debugging option is set, the contents of objects are
recorded in this log as they are freed.
.sp
If the "contents" debugging option was not set, 256 bytes of each freed buffer
are saved.
.RE

.sp
.ne 2
.na
\fB\fBfail\fR[=\fIsize\fR]\fR
.ad
.RS 22n
Records are entered into this log for every failed allocation.
.RE

For any of these options, if \fIsize\fR is not specified, the default value of
64k is used.  The \fIsize\fR parameter must be an integer that can be qualified
with K, M, G, or T to specify kilobytes, megabytes, gigabytes, or terabytes,
respectively.
.sp
Logs that are not listed or that have either a size of 0 or an invalid size are
disabled.
.sp
The log is disabled if during initialization the requested amount of storage
cannot be allocated.
.RE

.SH ATTRIBUTES
See \fBattributes\fR(7) for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
Interface Stability	Unstable
_
MT-Level	MT-Safe
.TE

.SH SEE ALSO
.BR mdb (1),
.BR abort (3C),
.BR signal (3C),
.BR umem_cache_create (3MALLOC),
.BR umem_setmtbf (3MALLOC),
.BR attributes (7)
.sp
.LP
\fIModular Debugger Guide\fR:
.sp
.LP
https://illumos.org/books/mdb/
.SH WARNINGS
When \fBlibumem\fR aborts the process using \fBabort\fR(3C), any existing
signal handler for \fBSIGABRT\fR is called. If the signal handler performs
allocations, undefined behavior can result.
.SH NOTES
Some of the debugging features work only for allocations smaller than 16
kilobytes in size. Allocations larger than 16 kilobytes could have reduced
support.
.sp
.LP
Activating any of the library's debugging features could significantly increase
the library's memory footprint and decrease its performance.
